Nicotine from tobacco is addictive, and it is a major health problem. In developed countries, smoking is the leading cause of premature deaths. In the United States, smoking-related illness causes more than 430,000 deaths and $50 billion in medical costs annually. Nicotine addiction has consequences on the health of the US population that are greater than the combined effects of all other addictive drugs (8,63,149,150). Dopamine (DA) systems are thought to play an important role in reinforcing rewarding behaviors, and drugs of addiction, such as nicotine, can alter or commandeer those systems. We will employ a combination of in vitro and in vivo techniques to study nicotinic cholinergic mechanisms that influence DA release both at the source and the target. We also will investigate how nicotine, as obtained from tobacco, alters the normal nicotinic cholinergic mechanisms that regulate the DA systems. Aim 1 will use patch-clamp electrophysiology applied to midbrain slices (VTA/SNc) to investigate nicotinic cholinergic mechanisms that modulate synaptic plasticity in the VTA/SNc (the DA source). Examining these issues should help us to understand the short-term and longer-term nicotinic influences over the firing of the midbrain neurons that supply DA. Aim 2 will use fast cyclic voltammetry and HPLC in striatal slices to investigate nicotinic influence over DA release in a target (the nucleus accumbens, NAc). Aim 3 will use in vivo unit recording and microdialysis with HPLC to examine the relationship between VTA/SNc activity and NAc activity or DA concentration. The relationship between VTA/SNc activity and downstream consequences in the NAc is a vital component of the addiction process. The experiments will investigate how endogenous nicotinic cholinergic mechanisms and exogenous nicotine modulate the activity of DA neurons in the midbrain and influence DA release in the striatum (particularly the NAc). The studies directly investigate developing theories of "reward" arising from new results. There is a complex (and not yet understood) relationship between the activity of midbrain DA neurons and the downstream consequences at the targets. The proposed research directly addresses DA's ro1e in reward mechanisms and examines the specific actions of nicotine that contribute to addiction